Hydro mechanical continuosusly variable transmission

ABSTRACT

The invention comprises a hydro-mechanical continuously variable transmission (HMCVT) that uses a planetary gear system to provide a combination of hydraulic and mechanical power for a vehicle or stationary equipment. The invention further comprises various ancillary elements to improve the performance of the HMCVT.

FIELD

This invention relates to a drive system useful as a vehicle propulsionsystem or stationary equipment drive, combining mechanical and hydraulicpower systems.

BACKGROUND

Hydraulic drive systems are commonly used for large vehicles orstationary equipment. However, as the output speed increases at a givengear setting, the efficiency of the hydraulic drive is correspondinglyreduced. This makes it inefficient to run hydraulic drives at the upperhalf of the gear setting. This problem may be overcome by havingmultiple gear settings, but the complexity of the resulting transmissionnegates the benefits of using a hydraulic drive.

An alternative to a hydraulic drive system is a mechanically drivensystem. However, conventional mechanical drive systems are limited todiscrete gear ratios, which do not allow for infinite speed ratios asfound in hydraulic drives. A great deal of power management between theengine and the transmission at all output speeds is necessary fortransmission effectiveness. A purely mechanical drive is inadequate toensure the efficient use of the engine's available power due to thediscrete speed ratios, while a purely hydraulic drive has inherentlypoor efficiency at higher operational speeds.

With the increasing costs of fuel and more stringent emissionsrequirements, there is a need for more efficient drive systems for largeand small vehicles, as well as stationary equipment, to replacetraditional hydraulic and mechanical drive systems.

It is an object of this invention to provide a more efficient drivesystem for large and small vehicles and stationary equipment bycombining hydraulic and mechanical power systems.

It is a further object of this invention to provide a transmissionsystem for optimizing use of combined drive systems.

It is a still further object of this invention to provide a combineddrive system with a dual or multiple speed, shift-on-the-fly gearbox forextended speed and torque ranges.

It is a still further object of this invention to provide an improvedsteering system for combined drive systems when applied to differentialoutput speed requirements.

SUMMARY

The invention comprises a hydro-mechanical continuously variabletransmission (HMCVT) that uses a planetary gear system to provide acombination of hydraulic and mechanical power for a vehicle orstationary equipment.

The HMCVT may also include a 2-speed planetary clutch system to expandthe operating parameters of the vehicle or stationary equipment.

The HMCVT may further include a planetary steering system that workswith or without the 2-speed planetary clutch system.

The HMCVT may also include a launch assist device to limit torqueapplied to the drive pump when the ratio of hydraulic pump displacementto hydraulic motor displacement is small.

The HMCVT may additionally include a lockup brake coupled to thehydraulic branch input, operative to lock out the hydraulic branch andforce all power through the mechanical branch when the transmissionoutput is operating at a pre-selected percentage of its maximum speed.The lockup brake may be combined with the launch assist device into asingle device.

The HMCVT may further include an anti-recirculating reverser deviceoperative to allow the transmission output to operate in a reversedirection of motion without developing a recirculating power flowthrough the mechanical branch.

The 2-speed planetary clutch, planetary steering system, launch assistdevice, lockup brake and anti-recirculating reverser device may be usedindividually or in any combination of two or more in any given HMCVT.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention itself, both as to organization and method of operation,as well as additional objects and advantages thereof, will becomereadily apparent from the following detailed description when read inconnection with the accompanying drawings:

FIG. 1 shows a planetary gear set with multiple planetary gears;

FIG. 2 shows a block diagram of an HMCVT in a RSC configuration with alloptional components;

FIG. 3 shows a block diagram of an HMCVT in a RSC configuration;

FIG. 4 shows a block diagram of an HMCVT in a SCR configuration;

FIG. 5 shows a block diagram of an HMCVT in a SRC configuration;

FIG. 6 shows a block diagram of an HMCVT in a RSC configuration with a2-speed clutch;

FIG. 7 shows a block diagram of an HMCVT in a RSC configuration with aplanetary steering system;

FIG. 8 shows a block diagram of an HMCVT in a RSC configuration with alaunch assist device;

FIG. 9 shows a block diagram of an HMCVT in a RSC configuration with alockup brake;

FIG. 10 shows a block diagram of an HMCVT in a RSC configuration with aspur gear reverser;

FIG. 11 shows a block diagram of an HMCVT in a RSC configuration with abevel gear reverser;

FIG. 12 shows a block diagram of an HMCVT in a RSC configuration with amechanical disconnect reverser;

DETAILED DESCRIPTION

The hydro-mechanical continuously variable transmission (HMCVT) isdesigned to split input power between a hydraulic drive branch, using ahydraulic pump and motor, and a parallel mechanical drive branch, usingshafts and/or gears, recombining the power from each branch into asingle output.

The HMCVT is based on a planetary gear set 10 as shown in FIG. 1. Aplanetary gear set 10 consists of four parts: a carrier gear 12, anumber of planetary gears 14, a ring gear 16 and a sun gear 18. The ringgear 16 and the sun gear 18 are connected through the planetary gears14. The planetary gears 14 are also connected to the carrier gear 12. InFIG. 1, three planetary gears 14 a-c are used, more may be used ifnecessary.

The planetary gear set 10 is connected to the hydraulic drive pump 22,the main shaft 26 and the transmission input 40. A 3 letter code (R=ringgear; S=sun gear; C=carrier gear) has been adopted for purposes of thisdiscussion to describe how the planetary gear set 10 is connected withinthe transmission: 1^(st) letter designates which part of planetary gearset 10 is connected to the hydraulic drive pump 22; 2^(nd) letterdesignates which part of planetary gear set 10 is connected to the mainshaft 26; the last letter designates which part of planetary gear set 10is connected to the input 40 from the engine.

A full HMCVT system in a RSC configuration with all optional componentsconnected is shown in FIG. 2. In the RSC configuration, a hydraulicdrive pump 22 is connected to the ring gear 16 of the planetary gear set10 and the sun gear 18 is connected to the combiner gear 20 via the mainshaft 26. The combiner gear 20 is also connected to a hydraulic drivemotor 24. The input 40 from the main engine (not shown) to the HMCVT isreceived by the carrier gear 12. A detailed view of the RSCconfiguration is shown in FIG. 3.

A full HMCVT system in a SCR configuration is shown in FIG. 4. In theSCR configuration, a hydraulic drive pump 22 is connected to the sungear 18 of the planetary gear set 10 and the carrier gear 12 isconnected to the combiner gear 20 via the main shaft 26. The combinergear 20 is also connected to a hydraulic drive motor 24. The input 40 tothe HMCVT is received by the ring gear 16.

A full HMCVT system in a SRC configuration is shown in FIG. 5. In theSRC configuration, a hydraulic drive pump 22 is connected to the sungear 18 of the planetary gear set 10 and the ring gear 16 is connectedto the combiner gear 20 via the main shaft 26. The combiner gear 20 isalso connected to a hydraulic drive motor 24. The input 40 to the HMCVTis received by the carrier gear 12.

In theory, the carrier gear 12, ring gear 16 and sun gear 18 may beconnected to the input 40, drive pump 22 and main shaft 26 in anycombination. However, the above three configurations have tested as themost practical for application as transmissions for large vehicles.

Mathematically, it can be shown that in the HMCVT, the power is splitsuch that the power from the hydraulic system (including the drive pump22 and the drive motor 24) combines with the mechanical system(including the main shaft 26) to equal 100% of the total powerlessefficiency losses. It can further be shown that the percentage ofmechanical power increases as the output speed increases, with acorresponding decrease in hydraulic power. The result is a moreefficient use of the input energy 40 than in a strictly hydraulic orstrictly mechanical transmission.

It can also be shown that the torque ratio between the ring gear 16 andthe sun gear 18 is only dependent on the gear ratio between the ringgear 16 and the sun gear 18. This means that the final gear ratio of theHMCVT can be set by the choice of ring gear 16 and sun gear 18.

To prove: define the following terms: h-hydraulic, m-mechanical,i-input, specific speed (O_(x)) is ratio of x (x=h,m,i) gear speed toinput (i) gear speed.

Define a constant R as the speed of the m-gear when the h-gear is notturning: R=O_(m)|O_(h)=0. Then define O_(m)=RS, where S reflects theactual speed of the output (as a value from 0 to 1). R and S are used tomake the equations independent of the actual configuration of theplanetary gear set 10.

Since O_(m) is linear in S, O_(h) must also be linear with S, as afunction of (1−S), since O_(h)=0 when S=1. At S=1/R, O_(m)=1. This meansthat at S=1/R the i-gear and m-gear are turning at the same speed.Considering the planetary gear model in FIG. 1, this means that the ringgear 16 and sun gear 18 are turning at the same speed. For this tooccur, the planetary gears 14 must not be turning, meaning that thecarrier gear 12 is also turning at the same speed as the ring gear 16and sun gear 18.

More generally, when any two of the gears of the planetary gear set 10are moving at the same speed, so is the third gear. Using this result,we then get O_(h)=(R/R−1) (1−S).

The power split then becomes P_(h)=1−S and P_(m)=S. This also means thattwo forms of power recirculation can occur: “overdrive” when S>1 and“reverse” when S<0.

In the physical HMCVT, the combiner gear 20 and planetary gear set 10are responsible for controlling the distribution of power between thedrive pump 22 and the drive motor 24. As the output speed changes, thepower split between the drive pump 22 and drive motor 24 is also changedas described above. When the output is motionless (speed=0), main shaft26 is also motionless (0 rpm). As the output moves, the drive pump 22must pump fluid and, initially, all the power is derived from the drivepump 22 and drive motor 24. As the output speed increases, the mainshaft 26 and the connected drive motor 24 (through the combiner gear 20)must turn faster. As a result, the drive pump gear (in the RSCconfiguration, ring gear 16) turns slower, due to the effect of theplanetary gear system 10 and the need to maintain a constant torqueratio.

A considerable advantage of the HMCVT lies in the unique ability of theconfigured systems as shown in FIGS. 2-5 to enable a driven output onboth ends of the transmission via a common shaft 26. This isparticularly useful in vehicles or stationary equipment that requireduplicated output shafts to two drives such as tracks and/ordifferentials.

Furthermore, one or both of the outputs can be engaged or disengagedeliminating the need for a transfer case when configured for multipleoutput drives.

The HMCVT speed can be controlled in any conventional manner, however anelectronic control system is preferred to best optimize the powersplitting in connection with the output speed. Furthermore, theelectronic control system can also include control means for thetwo-speed transmission system, planetary steering system, launch assistdevice, lockup brake and anti-recirculatory reverser discussed below.

Two-Speed Transmission

An additional modification to optimize the use of the HMCVT is atwo-speed planetary clutch system as shown in FIG. 6. The output 26 isconnected to the input of an additional 2-speed shifting planetary 30.Power enters the shifting planetary through the shifting planetary sungear 31 and exits through the shifting planetary carrier gear 35. In lowspeed operation, the shifting planetary ring gear 33 is held fixed by alow-speed clutch or brake 32, creating a reduction in the gear ratio.Shifting to high gear for high-speed operation is accomplished byreleasing the brake 32 and applying a high-speed clutch 34 toeffectively give a 1:1 gear ratio.

The 2-speed planetary clutch system provides an extended range ofavailable speeds and torques to the operator. The result is an increasedoperating envelope for the vehicle or stationary equipment.

Planetary Steering System

Another useful modification for the HMCVT is a planetary steering systemas shown in FIG. 7. As shown, power is sent from the main input 40 totwo steering planetaries 52, one for each output drive on either side ofthe transmission. The steering system also includes a closed-loophydraulic pump 54 that is driven in relation to the current engine RPM.The output of the pump 54 is connected to a hydraulic motor 56 thatdrives a cross shaft assembly referred to as a zero shaft 58.

The zero shaft 58 is connected to the sun gear 60 of the left and rightsteering planetaries 52 and the left and right sun gears 60 are drivenby the motor 56 in opposite directions. Therefore, when the zero shaft58 turns, the speed of the inside drive of the vehicle decreases and thespeed of the outside drive increases.

The result of the planetary steering system is a high-precision steeringsystem that provides quick reaction times while maintaining good drivingcharacteristics during straight-ahead motion.

Launch Assist Device (LAD)

One characteristic of the HMCVT is that at low output speeds, the pump22 is set to a very low displacement and the motor 24 is set to a highdisplacement. In theory, this could create a very large torquemultiplication through the hydraulic branch of the HMCVT. However, inthat scenario, the hydraulic pressures generated would exceed those thatcan be withstood by the system. Therefore, the hydraulic ratio must bereduced to limit pressure to acceptable levels. Unfortunately, thiscorrective measure also reduces the output torque at very low speeds.

To solve this problem, an energy absorber, called a Launch Assist Device(LAD) 70 is attached to the pump 22 as shown in FIG. 8. The LAD 70provides an initial resistance to the gear element of the planetary 10driving the hydraulic branch. This resistance limits the torqueavailable to the pump 22 and allows the mechanical branch to reach itsfull torque output at very low speeds. As a result, the torque isavailable at the output of the HMCVT.

The LAD 70 is only required at very low speeds and should be graduallyphased out as the speed increases. As shown, the LAD 70 is a modulatedbrake assembly. However, other devices, such as a fluid coupling or atorque converter, could be used.

Lockup Brake

At the upper limit of the HMCVT operating range, the displacement ratiobetween the motor 24 and the pump 22 decreases to the point where theamount of torque available to the pump 22 is insufficient to keep itturning. With the speed of the hydraulic pump 22 at zero, all the poweris transferred exclusively through the mechanical branch. Unfortunately,most currently available pump and motor designs include some degree ofinternal leakage, preventing the HMCVT from reaching a pure 100%mechanical state.

This problem can be solved by using a lockup brake 80 as shown in FIG. 9to prevent the pump 22 from turning at the end of the operating range.The lockup brake 80 is attached to one of the gears 10 driving the pump22. When the upper end of the operating range is reached, the lockupbrake 80 is activated, forcing the HMCVT into a pure 100% mechanicalmode. The lockup brake 80 can then be deactivated when the HMCVToperating range falls out of the upper regions. Theactivation/deactivation point for the lockup brake 80 will be determinedby the operating conditions and parameters for the vehicle or stationaryequipment using the HMCVT.

Anti-Recirculatory Reverser

The simplest way to reverse the direction of the final output of thetransmission is to reverse the drive motor. When this happens, the powerin the mechanical branch is negative and the power in the hydraulicbranch is greater than the input power. What is effectively happening isthat the drive motor must reverse the direction of the mechanical outputof the split speed, feeding power upstream through the mechanicalbranch. To balance out the power equations, the hydraulic branch musttransfer an amount of power equal to the input plus the recirculatedpower from the mechanical branch.

In order to accommodate the increased power levels, both the hydraulicand the mechanical branches must have increased component strengthand/or size, which is not always practical or desirable. Therefore, anadditional reverser subsystem that avoids the need to reinforce thehydraulic is desirable.

One potential reverser subsystem 90 as shown in FIGS. 10 and 11 involvesthe installation of a reversible gear at the input. The input 40 isconnected to a sliding clutch/synchronizer assembly 90. Depending onwhich gear is engaged with the clutch/synchronizer 90, the HMCVTcomponents, including the drive pump 22 and motor 24, will rotate ineither the forward or reverse direction. Either spur gears (FIG. 10) orbevel gears (FIG. 11) can be used in the clutch/synchronizer 90,however, bevel gears allow for a 90-degree change between the enginepower output and the main axes of the transmission (the final poweroutput). In either case, if steering planetaries 52 (see FIG. 7) arepresent, they are connected to the power output through a preset gearratio and a constant direction so that the steering will functionregardless of the forward/reverse direction of the clutch/synchronizer90.

An alternative subsystem for the reverser shown in FIG. 12 disconnectsthe mechanical branch during reverse hydraulic operation and locks themechanical output to the transmission housing (not shown). In this case,the input shaft always rotates in the same direction. The mechanicaloutput may be selectively coupled to either the main shaft 26 or thetransmission housing by means of a clutch/synchronizer assembly 112.When the mechanical output is connected to the main shaft 26, forwardoutput speeds result. When the mechanical output is connected to thehousing, the mechanical branch is locked out of the transmission.Reverse output speeds can then be achieved by reversing the direction ofthe drive motor. Power flows exclusively through the hydraulic branchand cannot be recirculated back through the mechanical branch.

Accordingly, while this invention has been described with reference toillustrative embodiments, this description is not intended to beconstrued in a limiting sense. Various modifications of the illustrativeembodiments, as well as other embodiments of the invention, will beapparent to persons skilled in the art upon reference to thisdescription. It is therefore contemplated that the appended claims willcover any such modifications or embodiments as fall within the scope ofthe invention.

1. A hydro-mechanical continuously variable transmission for a vehicleor stationary equipment, comprising: a) a planetary gear set having atleast a ring gear, a sun gear and a carrier gear; b) a main power inputcoupled to one of said ring gear, said sun gear and said carrier gear;c) a combiner gear coupled to a main output shaft; d) a hydraulic branchhaving a hydraulic pump, said hydraulic branch receiving an input from asecond one of said ring gear, said sun gear and said carrier gear andsending an output to said combiner gear; e) a mechanical branchreceiving an input from a third one of said ring gear, said sun gear andsaid carrier gear and sending an output to said main shaft; wherein saidcombiner gear acts to combine said output from said hydraulic branchwith said output from said mechanical branch at said main output shaftsuch that said transmission decreases the percentage of main powerarising from said hydraulic branch as main output shaft increases inspeed.
 2. A transmission according to claim 1, wherein said hydraulicdrive branch comprises a variable displacement hydraulic pump connectedin a closed-loop circuit with a variable displacement hydraulic motorcapable of providing a variable input/output torque ratio byindependently varying displacement of said hydraulic pump and saidhydraulic motor.
 3. A transmission according to claim 1, wherein saidmechanical branch has a fixed gear ratio and a fixed input/output torqueratio.
 4. A transmission according to claim 1, further comprising one ormore additional elements selected from the group consisting of: a) aspeed control device to increase the operating range of the vehicle orstationary equipment, consisting of a two-speed power shift transmissioncoupled to said main shaft, with a low gear to increase torque at lowoutput speeds and a high gear to allow for a higher maximum outputspeed; b) a launch assist device to limit torque applied to saidhydraulic branch at low output speed, comprising an energy absorptiondevice connected to said hydraulic branch input and a control device tocontrol the amount of energy absorption; c) a lockup brake coupled tosaid hydraulic branch input, operative to lock out said hydraulic branchand force all power through said mechanical branch when said main outputshaft is operating at a pre-selected percentage of its maximum speed; d)a planetary steering system comprising: i) a hydraulic pump; ii) ahydraulic motor; iii) a zero shaft assembly with one input coupled tosaid hydraulic motor and two outputs geared to rotate at the same speedin opposite directions; and iv) two planetary gear sets with identicalgear ratios aligned coaxially with said main shaft, an input for eachplanetary gear set coupled to one of said zero shaft outputs, a secondinput for each planetary gear set coupled to said main shaft and anoutput for each of said planetary gear sets directed to opposite sidesof said vehicle or stationary equipment, said hydraulic pump andhydraulic motor operative to control the amount of power available forsaid zero shaft; e) an anti-recirculating reverser device operative toallow said main output shaft to operate in a reverse direction of motionwithout developing a recirculating power flow through said mechanicalbranch; and f) a combination of elements a), b), c), d) and e).
 5. Thetransmission according to claim 4, wherein said high gear of said speedcontrol device is a 1:1 ratio gear.
 6. The transmission according toclaim 4, wherein said energy absorption device is a friction-baseddevice.
 7. The transmission according to claim 4, wherein said energyabsorption device is a hydrodynamic device.
 8. The transmissionaccording to claim 4, wherein said launch assist device and said lockupbrake are combined into a single device.
 9. The transmission accordingto claim 4, wherein said anti-recirculatory reverse comprises aclutch/synchronizer assembly coupled to said mechanical power output,said clutch assembly operative to selectively engage said main shaft forforward output operation, a housing of said transmission for reverseoutput operation, and nothing for neutral output operation, such that inreverse output operation said mechanical output is prevented fromrotating and power flows solely through said hydraulic branch.
 10. Thetransmission according to claim 4, wherein said anti-recirculatorydevice comprises a clutch/synchronizer coupled to said main power input,said clutch/synchronizer having two gears located coaxially on eitherside of said clutch/synchronizer, each of said gears driving a geartrain of equal and opposite gear multiplication, said gear trainscoupled to one of said planetary gears and forward, neutral and reverserotation of said main output shaft determine by said clutch/synchronizerengaging one of said two gears, the other of said two gears and neitherof said two gears, respectively.
 11. The transmission of claim 10,wherein said clutch/synchronizer uses spur gears.
 12. The transmissionof claim 10, wherein said clutch/synchronizer uses bevel gears.
 13. Ahydro-mechanical continuously variable transmission for a vehicle orstationary equipment, comprising: a) a planetary gear set, having a ringgear, a sun gear and a carrier gear; b) a single main power inputconnected to one of the ring gear, sun gear or carrier gear; c) a mainoutput shaft coupled to a combiner gear, which can provide main poweroutput on either side of said main output shaft; d) a hydraulic drivebranch, comprising a variable displacement hydraulic pump connected in aclosed-loop circuit with a variable displacement hydraulic motor capableof providing a variable input/output torque ratio by independentlyvarying displacement of said hydraulic pump and said hydraulic motor,said hydraulic pump receiving a power input from one of the ring gear,sun gear or carrier gear different from the one connected to said mainpower input, and said hydraulic drive branch providing a hydraulic poweroutput to said combiner gear; and e) a mechanical drive branch,comprising a fixed gear ratio and a fixed input/output torque ratio,said mechanical drive branch receiving a power input from a remainingone of the ring gear, sun gear or carrier gear, and said mechanicaldrive branch providing a mechanical power output to said main outputshaft; wherein said combiner gear acts to combine the torques from saidhydraulic branch and said mechanical branch to provide said main poweroutput from said main shaft and wherein overall torque/speed ratios forsaid transmission are controlled by said displacement of said hydraulicpump and said hydraulic motor, with a microprocessor controlling theratio of hydraulic pump displacement to hydraulic motor displacement,and wherein said transmission decreases the percentage of main powerarising from said hydraulic branch as said main output shaft increasesin speed.
 14. The transmission according to claim 13, further comprisingone or more additional elements selected from the group consisting of:a) a speed control device to increase the operating range of the vehicleor stationary equipment, consisting of a two-speed power shifttransmission coupled to said main shaft, with a low gear to increasetorque at low output speeds and a high gear to allow for a highermaximum output speed; b) a launch assist device to limit torque appliedto said drive pump when said ratio of hydraulic pump displacement tohydraulic motor displacement is small, comprising an energy absorptiondevice connected to said hydraulic branch input and a control device tocontrol the amount of energy absorption; c) a lockup brake coupled tosaid hydraulic branch input, operative to lock out said hydraulic branchand force all power through said mechanical branch when said main outputshaft is operating at a pre-selected percentage of its maximum speed; d)a planetary steering system comprising: i) a hydraulic pump; ii) ahydraulic motor; iii) a zero shaft assembly with one input coupled tosaid hydraulic motor and two outputs geared to rotate at the same speedin opposite directions; and iv) two planetary gear sets with identicalgear ratios aligned coaxially with said main shaft, an input for eachplanetary gear set coupled to one of said zero shaft outputs, a secondinput for each planetary gear set coupled to said main shaft and anoutput for each of said planetary gear sets directed to opposite sidesof said vehicle or stationary equipment, said hydraulic pump andhydraulic motor operative to control the amount of power available forsaid zero shaft; e) an anti-recirculating reverser device operative toallow said main output shaft to operate in a reverse direction of motionwithout developing a recirculating power flow through said mechanicalbranch; and f) a combination of elements a), b), c), d) and e).
 15. Thetransmission according to claim 14, wherein said high gear of said speedcontrol device is a 1:1 ratio gear.
 16. The transmission according toclaim 14, wherein said energy absorption device is a friction-baseddevice.
 17. The transmission according to claim 14, wherein said energyabsorption device is a hydrodynamic device.
 18. The transmissionaccording to claim 14, wherein said launch assist device and said lockupbrake are combined into a single device.
 19. The transmission accordingto claim 14, wherein said anti-recirculatory reverse comprises aclutch/synchronizer assembly coupled to said mechanical power output,said clutch assembly operative to selectively engage said main shaft forforward output operation, a housing of said transmission for reverseoutput operation, and nothing for neutral output operation, such that inreverse output operation said mechanical output is prevented fromrotating and power flows solely through said hydraulic branch.
 20. Thetransmission according to claim 14, wherein said anti-recirculatorydevice comprises a clutch/synchronizer coupled to said main power input,said clutch/synchronizer having two gears located coaxially on eitherside of said clutch/synchronizer, each of said gears driving a geartrain of equal and opposite gear multiplication, said gear trainscoupled to one of the ring gear, sun gear or carrier gear and forward,neutral and reverse rotation of said main output shaft determined bysaid clutch/synchronizer engaging one of said two gears, the other ofsaid two gears and neither of said two gears, respectively.
 21. Thetransmission of claim 20, wherein said clutch/synchronizer uses spurgears.
 22. The transmission of claim 20, wherein saidclutch/synchronizer uses bevel gears.